| 摘要 |
The boom has a base box (1) in which multiple inner boxes are guided coaxial to each other. A head (8) is provided with or without a deflection roller in an inner most inner box at an outer sided end. A bolting fork (3) is arranged at an inner side of the head, and is opened forward in a diametrical opposed manner, where a locking bolt (4) of an intermittent new inner box (2) is inserted into center of the bolting fork. A telescopic system with a safety-and bolting device is inserted/extended for coupling the inner box (2) upto a position of the locking bolt.
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